The present invention generally relates to ultrasound imaging. In particular, the present invention relates to a system and method for range dependent weighting for ultrasound spatial compound imaging.
Conventional ultrasound imaging systems acquire ultrasound images of the same anatomy at several angles. Data from these images are then combined to form a single, composite image such as a spatially compounded image. The combination of the image data may occur using equal contributions from each image (for example, using equal weighting of image data from all images). The combination of the image data may also occur by using a greater data contribution from some images (for example, using greater weighting of image data from some images) and lesser data contributions from other images (for example, using lesser weighting of image data from some images).
For example, conventional imaging systems may employ regional input frame weighting. FIG. 6 illustrates a schematic diagram demonstrating regional input frame weighting. A transducer array receives ultrasound beams, which may be employed to generate one or more of input frames 610, 620, 630. Each of input frames 610, 620, 630 can be obtained at different angles, or steering angles. For example, input frame 610 is a left steered frame, input frame 620 is a non-steered frame and input frame 630 is a right steered frame.
The three image frames 610, 620, 630 may be combined into a compounded image. Image data sections 641, 643, 645, 647, 649 represent the combined image data from frames 610, 620, 630. Data sections 643, 645, 647 represent the spatially compounded image. Due to the shape of image frames 610, 620, 630, data section 643 includes image data from frames 610 and 620, data section 647 includes image data from frames 620 and 630, and data section 645 includes image data from frames 643, 645, and 647.
With equal weighting and normalization to provide uniform image brightness, a spatially compounded image typically includes 50% of image data from frames 610 and 620 for image data sections 643 and 647. Similarly, the compounded image typically includes 33% of image data from frames 610, 620 and 630.
If all three frames 610, 620, 630 have equal weighting (for example, regional input weighting is not applied), the left edge of the right steered frame 630 and the right edge of the left steered frame 610 can be visible in the compounded image (represented by data sections 643, 645, 647), especially if there is probe or anatomical motion. This visibility may be mitigated by reducing the weighting of the right steered image frame 630 as it gets closer to the left edge of the data section 645 and increasing the corresponding weighting of the image data from frames 620 and 610 in the same data section 645.
However, the near field portion of compounded ultrasound images often suffer from image artifacts caused by the reverberation of ultrasound beam waveforms off of common near field anatomical structures. The near field portion generally includes portions of an anatomy relatively close to the surface of the anatomy, such as a patient's skin. Near field anatomical structures causing such reverberation typically include fat layers and muscle, for example. Such structures are typically perpendicular to ultrasound waveforms in the near field.
Current ultrasound imaging systems may scan the imaged anatomy at multiple angles, as described above. The angled beam firings generate less reverberation artifacts. By weighting the higher-angled image frames more and lesser-angled frames less in the compound image, the effects of reverberation can be reduced. As reverberation is only an imaging problem in the near field, applying range-dependent weighting of image frames can be applied to further reduce reverberation artifacts in spatially compounded images. Reducing the amount of data being used to generate the compound image in the near field results in a lower level of compounding in the near field compared to the rest of the image. Range-dependent weighting can allow near field artifacts to be reduced without sacrificing any aspect of the image in the mid- and far fields. Such weighting can make the speckle pattern over the image range more uniform.
In addition, range-dependent weighting can provide for a more uniform image over an image range. Curved linear probes, by nature of their geometry, result in image vectors that are closer together in the near field and then spread out with depth. At typical image spacing, this results in the near-field speckle pattern that is finer than the far field speckle pattern. Spatial compounding has the effect of smoothing out the speckle pattern in the image. Because the near field speckle pattern is already finer than the mid and far field, the compounding image can appear much smoother in the near field than in the far field. Meanwhile, due to the limited size of probe apertures, an image usually looks un-focused and blurred in the far field. The blurriness can be further amplified by spatial compounding. The image may therefore not have a uniform appearance in range and may consequently not be well received by a user. By applying range-dependent weighting to image data, a more uniform image may be produced. Specifically, by reducing the contribution of image data from certain angles in the near field, less speckle reduction may be achieved. In addition, by reducing the contribution of certain angles in the far field can cause less blurring. Combining these two can result in a more uniform image.
Thus, a need exists for a system and method for range dependent weighting in ultrasound spatial compound imaging. Such a system and method can provide for a reduction in image artifacts caused by waveform reverberation from near field anatomical structures. In addition, such a system and method can make a speckle pattern of an ultrasound image more uniform over the image range.